You have to make a good print first. Then you read a point on that negative with the analyzer and set that to a standard. When you print a new negative, you pick a point close to the same color and use those settings to adjust the filter pack. That is one type. Another type looks at the entire print and integrates the color and assumes it to be overall neutral gray. If that makes a good print, then the assumption is continued and if a negative integrates as other than gray, the analyzer suggests a change.

I don't use one. It is too cumbersome and expensive. It is also error prone to novice users. Color negative films give me the same results for the last 60 years for filter pack with modern papers.